If you don't play close attention to him singing you won't know it's him his voice changed drastically in the mid 80's I think Josky helped in an immense way regarding singing.
Agreed, starting with Ngounda he starting incorporating softer melody with his singing. Songs like Farousci, L'homme de La Rue, and Diva are good examples highlighting the difference versus the late 70s releases.
For someone very young at the time, Koffi was very fortunate to have collaborated with most of the popular musicians/groups of the time. My first time hearing Longomo in a long time.